Macular degeneration is a disease of the retina which affects over thirteen million people in the United States and is characterized by loss of central vision due to the loss of photoreceptors in the central part of the retina, the macula lutea. D""Amico et al. (1994) New England J. Med. 331:95-106 and Kliffen et al. (1997) Microscopy Res. and Techniq. 36:106-122. The macula is the most important part of the eye for high resolution vision because there is a greater concentration of cone type photoreceptors which are responsible for color vision and visual acuity.
Photoreceptor cells, especially rod cells, renew their outer segments at a high rate. Thus, as new lamellae discs are formed and added to the photoreceptor cells, the older lamellae discs at the tip are discarded. Retinal pigment epithelial (RPE) cells function to provide support for the retinal photoreceptors and are responsible for the metabolic digestion of the discarded outer segments of the neural retina. Thus, RPE cells are responsible for the phagocytosis and digestion of the discarded discs at a turn over rate of approximately 30-100 discs each day. Underlying the RPE cells is the choriocapillaris which contains the vasculature to provide nutrients and remove metabolic by-products from the retina.
In macular degeneration, the RPE cells are dysfunctional, thereby leading to a build up of metabolic by-products, including discarded discs in the retina. The presence of metabolic debris and excess fluid in the retina damage photoreceptor cells, thereby compromising visual acuity. Cingle et al. (1996) Curr. Eye. Res. 15:433-438 and Curcio et al. (1996) Invest. Ophthal. and Vis. Sci. 37:1236-1249. In addition, the degeneration of the RPE layer is also reflected by ensuing atrophy of the choriocapillaris.
In the dry form of macular degeneration, loss of vision is gradual and is associated with retinal pigment changes, deposits in the subretinal space called drusen, atrophy of the blood vessels supplying the retina and ultimately geographic atrophy in the absence of neovascularization. Although this form of macular degeneration has a slower progression to blindness, it is far more common, accounting for approximately 90% of the cases of acute macular degeneration. In the wet form of the disease, vessels arise from the choriocapillaris and penetrate Bruch""s membrane and the RPE cell layer to impinge upon the neural retina where they cause damage that leads to loss of central vision. Patients with the wet form of the disease are at high risk for subretinal neovascularization, geographic atrophy and retinal pigment epithelial detachment, all of which result in a rapid and severe loss of visional acuity.
Currently, there are few therapeutic alternatives for patients diagnosed with macular degeneration. Laser photocoagulation has been used for some cases of the wet form of the disease, but the clinical experience with this therapy has not been promising. If the retinal damage is close to the fovea, laser therapy is withheld to avoid potential loss of central photoreceptors. Lambert et al. (1992) Am. J. Ophthalmol. 113:257-262. In addition, radiation and photodynamic therapy has been performed for cases where neovascularization is diffuse or too severe. Although follow-up data showed an advantage of laser photocoagulation, reoccurrence of neovascularization occurred in over half of the patients, thereby undermining the initial benefit of the treatment. Macular Photocoagulation Study Group (1993) Arch. Ophthalmol. 111:1200-1209.
Opthalmic surgery can also be performed to remove neovascularization in the wet form of macular degeneration. Although this surgery has been reported to reduce the progression of the disease, restoration of visual acuity is limited.
The other competitive approach to treating macular degeneration is surgical implantation of human RPE cells. Although early clinical analysis has been promising, broader clinical application of human transplants to patients with macular degeneration will be extremely limited by the availability of human donors. Thus, a need exists for alternative sources of retinal cells and methods of retinal transplantation which can minimize the damage caused by retinal disorders such as macular degeneration.
The instant invention pertains to an isolated retinal cell or an isolated population of retinal cells suitable for transplantation into an allogeneic or xenogeneic subject, particularly a human subject. The retinal cells of the invention include neural retinal cells (e.g., rod or cone photoreceptor cells), retinal pigment epithelial (RPE) cells, iris epithelial cells and retinal stem cells (e.g., retinal progenitor cells). Thus, one aspect of the invention pertains to a transplantable composition for use in a subject comprising a retinal cell (e.g., a neural retina cell, RPE cell or iris epithelial cell) obtained from a pig, e.g., a fetal pig.
The porcine retinal cells of the invention include porcine neural retinal cells, retinal pigment epithelial (RPE) cells, iris epithelial cells and their precursors. Typically, these retinal cells are obtained from fetal pigs during selected stages of gestational development. For example, it has been determined that fetal retinal cells obtained from a fetal pig between about days 30 and 100, more preferably about days 40 and 90, and still more preferably about days 50 and 80, and yet more preferably about days 60 and 70, and most preferably about day 60-65 of gestation are suitable for transplantation into xenogeneic subjects, particularly human subjects.
Another aspect of the invention pertains to a porcine retinal cell or a population of retinal cells which are obtained from a pig predetermined to be free from at least two organisms which originate in pigs and which are capable of transmitting infection or disease to a xenogeneic recipient, e.g., a human, of the cells.
Categories of organisms from which the cells are free can include zoonotic, cross-placental, neurotropic, and/or ocular-infecting organisms. Within each of these categories, the organism can be a parasite, bacteria, mycoplasma, and/or a virus. In one embodiment, the retinal cells are free of one or more of the following organisms found in pigs: Toxoplasma, eperythrozoon, brucella, listeria, mycobacterium TB, leptospirillum, hemophilus suis, M. Hypopneumonia, porcine respiratory reproductive syndrome, rabies, pseudorabies, parvovirus, encephalomyocarditis virus, swine vesicular disease, teschen (Porcine polio virus), hemagglutinating encephalomyocarditis, suipoxvirus, swine influenza type A, adenovirus, transmissible gastroenteritis virus, bovine viral diarrhea, and vesicular stomatitis virus.
In another aspect of the invention, the retinal cell, in unmodified form, has at least one antigen on the cell surface which is capable of stimulating an immune response against the cell in a xenogeneic subject, for example, a human. The antigen on the surface of the retinal cell is altered to inhibit rejection of the cell when introduced into a xenogeneic subject. In one embodiment, the cell surface antigen which is altered is an MHC class I antigen. This MHC class I antigen can be contacted, prior to transplantation into a xenogeneic subject with at least one anti-MHC class I antibody, or a fragment or derivative thereof, which binds to the MHC class I antigen on the cell surface but does not activate complement or induce lysis of the cell. One example of an anti-MHC class I antibody is an anti-MHC class I F(abxe2x80x2)2 fragment, such as an anti-MHC class I F(abxe2x80x2)2 fragment of a monoclonal antibody PT85. The retinal cells can further be screened as described above such that the cells are isolated from a pig predetermined to be essentially free of organisms which are capable of being transmitted to a xenogeneic subject, e.g., a human subject.
Another aspect of the invention features a composition comprising a porcine retinal cell, e.g., a porcine neural retina cell, RPE cell or iris epithelial cell, and an antibody which binds an antigen on the surface of the porcine retinal cell. The composition can further comprise a pharmaceutically acceptable carrier.
This invention also provides methods for treating a retinal disorder in a subject by administering to the subject having the disorder a composition comprising the retinal cells of the invention, e.g., neural retina cells, RPE cells or iris epithelial cells, into the retina of the subject.
In one embodiment, the retinal disorder of a subject, e.g., a human, is treated by administering to the subject a composition comprising a porcine neural retina cell into the retina, e.g., subretinal space, of the subject. The method can be used to treat retinal disorders such as retinis pigmentosa, phototoxic retinopathy, light damaged retina or macular degeneration. In another embodiment, the retinal disorder of a subject, e.g., a human, is treated by administering to the subject a composition comprising a porcine RPE cell into the retina, e.g., subretinal space, of the subject. This method can be used to treat retinal disorders such as macular degeneration, gyrate atrophy, fundus flavimaculatus, Best""s disease, Sorsby""s dystrophy or Stargardt""s disease. The RPE cells can be administered to the subject in a cell suspension or can be administered as an intact sheet.
The compositions of the invention can further comprise a pharmaceutically acceptable carrier. In one embodiment, the porcine retinal cells, e.g., neural retinal cells, RPE cells or iris epithelial cells, which can be administered to a subject having a retinal disorder are porcine retinal cells which, in unmodified form, have at least one antigen on the cell surface which is capable of stimulating an immune response against the cell in a subject, e.g., a xenogeneic subject, e.g., a human. The antigen on the surface of the porcine retinal cell is altered to inhibit rejection of the cell when introduced into the subject. Examples of retinal cell surface antigens and methods of altering such antigens are described herein. Preferred retinal cell ages are also described herein. In another embodiment, the porcine retinal cells which can be administered to a subject having a retinal disorder are porcine retinal cells, e.g., neural retina cells, RPE cells or iris epithelial cells, which are obtained from a pig predetermined to be free from at least two organisms which originate in pig and which are capable of transmitting infection or disease to a xenogeneic recipient, e.g., a human, of the cells. Pathogen-free pigs are described in detail herein.
Other features and advantages of the invention will be apparent from the following detailed description and claims.
This invention features retinal cells suitable for introduction into an allogeneic or xenogeneic recipient, particularly a human subject. As used herein the phrase xe2x80x9cretinal cellxe2x80x9d includes neural retinal cells (also referred to herein as photoreceptor cells), retinal pigment epithelial (RPE) cells, iris epithelial cells, and their precursors. In a preferred embodiment, the retinal cells are mammalian retinal cells, e.g., porcine retinal cells or human retinal cells. The terms xe2x80x9cprecursorxe2x80x9d, xe2x80x9cprogenitorxe2x80x9d, and xe2x80x9cstem cellxe2x80x9d are used interchangeably herein and refer to cells which are multipotent, i.e., are capable of developing into a many different cell types, including neural retina cells, RPE cells and/or iris epithelial cells. xe2x80x9cRetinal pigment epithelial (RPE) cellsxe2x80x9d, as used herein refer to cells of the outermost external layer of the retina. RPE cells function to provide support for the retinal photoreceptors and are responsible for the metabolic digestion of the discarded outer segments of the neural retina. xe2x80x9cNeural retina cellsxe2x80x9d, as used herein, refer to the layer of photoreceptor cells (i.e., rod and cone cells) underlying the RPE cell layer in the retina. Neural retina cells are modified light sensitive neurons. Such precursor cells can be used as sources of the mammalian retinal cells of the invention, i.e., the retinal cells of the invention can be derived from such precursor cells. As used herein, the term xe2x80x9cderivedxe2x80x9d refers to cells which develop or differentiate from or have as ancestors multipotent precursor cells. These multipotent precursor cells are typically obtained from the eye cup and are cultured in vitro as described, for example, in Sheedlo et al. (1996) J. Neuroscience Res. 44:519-531, the contents of which are incorporated herein by reference, to generate the cells of the present invention. Thus, in one aspect of the invention, the retinal precursor cells of the invention are induced to differentiate in vitro prior to use in the compositions of the invention.
For example, porcine fetuses can be removed from a pregnant sow at gestational ages at which the retinal cells have not committed to specific cell fates. In one embodiment, stem cells are obtained from porcine embryos in early stages of development (e.g., starting at about day 30 of gestation) and cultured under conditions which promote proliferation. Agents, e.g., retinoic acid, butyrate, triiodo-thyronine, basic fibroblast growth factor, transforming growth factor, and s-laminin, which promote differentiation of these stem cells into retinal cell types, e.g., such as those described herein, can then be added to the culture. The resultant differentiated retinal cells can be transplanted into a recipient subject as described herein.
A. Modified Retinal Cells and an Isolated Population of Modified Retinal Cells
Retinal cells of the invention can be obtained from hemisecting the globe of the pig retina at the ora serrata and the anterior segment. Preferably, the cells are obtained from the neural retina or the eye cup of the porcine retina. In unmodified form, the retinal cell, i.e., the neural retina cell, RPE cell or iris epithelial cell, has at least one antigen on the cell surface which is capable of stimulating an immune response against the cell in an allogeneic or xenogeneic subject. To inhibit rejection of the cell when introduced into the subject, the antigen on the cell surface is altered prior to transplantation. In an unaltered state, the antigen on the cell surface stimulates an immune response against the cell when the cell is administered to a subject (also referred to herein as recipient or recipient subject). By altering the antigen, the normal immunological recognition of the retinal cell, e.g., a porcine retinal cell, by the immune system cells of the recipient is disrupted and additionally, xe2x80x9cabnormalxe2x80x9d immunological recognition of this altered form of the antigen can lead to retinal cell-specific long term unresponsiveness in the recipient. It is likely that alteration of an antigen on the retinal cell prior to introducing the cell into a subject interferes with the initial phase of recognition of the retinal cell by the cells of the host""s immune system subsequent to administration of the cell. Furthermore, alteration of the antigen may induce immunological nonresponsiveness or tolerance, thereby preventing the induction of the effector phases of an immune response (e.g., cytotoxic T cell generation, antibody production etc.) which are ultimately responsible for rejection of foreign cells in a normal immune response. As used herein, the term xe2x80x9calteredxe2x80x9d encompasses changes that are made to at least one retinal cell antigen(s) which reduces the immunogenicity of the antigen to thereby interfere with immunological recognition of the antigen(s) by the recipient""s immune system. In a preferred embodiment, at least one antigen on a porcine retinal cell, e.g., neural retina cell, RPE cell or iris epithelial cell, is altered such that upon introduction into a subject, e.g., a human, rejection of the cell is inhibited.
Antigens to be altered according to the current invention include antigens on a retinal cell, e.g., a porcine retinal cell, which can interact with an immune cell in a xenogeneic (or allogeneic) recipient subject and thereby stimulate a specific immune response against the retinal cell in the recipient. The interaction between the antigen and the immune cell may be an indirect interaction (e.g., mediated by soluble factors which induce a response in the immune cell, e.g., humoral mediated) or, preferably, is a direct interaction between the antigen and a molecule present on the surface of the immune cell (i.e., cell-cell mediated). As used herein, the term xe2x80x9cimmune cellxe2x80x9d is intended to include a cell which plays a role in specific immunity (e.g., is involved in an immune response) or plays a role in natural immunity. Examples of immune cells include all distinct classes of lymphocytes (T lymphocytes, such as helper T cells and cytotoxic T cells, B lymphocytes, and natural killer cells), monocytes, macrophages, other antigen presenting cells, dendritic cells, and leukocytes (e.g., neutrophils. eosinophils, and basophils). In a preferred embodiment, the antigen is one which interacts with a T lymphocyte in the recipient (e.g., the antigen normally binds to a receptor on the surface of a T lymphocyte).
In one embodiment, the antigen on the retinal cell to be altered is an MHC class I antigen. Alternatively, an adhesion molecule on the cell surface, such as NCAM-1 or ICAM-1, can be altered. An antigen which stimulates a cellular immune response against the cell, such as an MHC class I antigen, can be altered prior to transplantation by contacting the cell with a molecule which binds to the antigen. A preferred molecule for binding to the antigen is an antibody, or fragment thereof (e.g., an anti-MHC class I antibody, or fragment thereof, an anti-ICAM-1 antibody or fragment thereof, an anti-LFA-3 antibody or fragment thereof, or an anti-xcex22 microglobulin antibody or fragment thereof). A preferred antibody fragment is an F(abxe2x80x2)2 fragment. Polyclonal or, more preferably, monoclonal antibodies can be used. Other molecules which can be used to alter an antigen (e.g., an MHC class I antigen) include peptides and small organic molecules which bind to the antigen. Furthermore, two or more different epitopes on the same or different antigens on the cell surface can be altered. A particularly preferred monoclonal antibody for alteration of MHC class I antigens on porcine retinal cells is PT85 (commercially available from Veterinary Medicine Research Development, Pullman Wash.). PT85 can be used alone to alter MHC class I antigens or, if each antibody is specific for a different epitope, PT85 can be used in combination with another antibody known to bind MHC class I antigens to alter the antigens on the cell surface. Suitable methods for altering a surface antigen on a cell for transplantation are described in greater detail in Faustman and Coe (1991) Science 252:1700-1702 and PCT publication WO 92/04033. Methods for altering multiple epitopes on a surface antigen on a cell for transplantation are described in greater detail in PCT publication WO 95/26741, published on Oct. 12, 1995, the contents of which are incorporated herein by reference.
In another embodiment, the porcine retinal cells of the present invention can be modified to inhibit natural antibody-mediated hyperaeute rejection of the cells. For example, the retinal cells of the invention may, in unmodified form, express an epitope on their surface which stimulates hyperacute rejection of the retinal cells by natural antibodies in a recipient subject. Such an epitope can be altered, reduced or substantially eliminated. This treatment of the retinal cells inhibits subsequent recognition of the epitope by natural antibodies in a recipient, thereby inhibiting hyperacute rejection. In a preferred embodiment, the epitope is a carbohydrate, preferably galactosyl (xcex11,3)galactose (Gal (xcex11,3) Gal).
Epitopes on the surface of the retinal cells, e.g., neural retinal cells, RPE cells or iris epithelial cells, in one embodiment of the invention, are removed from the surface of a cell, such as by enzymatic or chemical treatment of the cell. For example, Gal (xcex11,3)Gal epitopes can be cleaved from a cell surface by treatment of the cell with an alpha-galactosidase. In another embodiment, formation of the epitope on the cell surface is inhibited. This can be accomplished by inhibiting the activity of an enzyme which forms the epitope. For example, formation of Gal (xcex11,3)Gal epitopes on the surface of a cell can be interfered with by inhibiting the activity of an alpha-1,3-galactosyltransferase within the cell, such as by introducing into the cell a nucleic acid which is antisense to a coding or regulatory region of an alpha-1,3-galactosyltransferase gene or by treating the cell with a chemical inhibitor of the enzyme. In yet another embodiment, epitopes on the surface of a retinal cell are altered by binding a molecule to the epitope, thereby inhibiting its subsequent recognition by natural antibodies in a recipient. For example, lectins, antibodies or antibody fragments can be bound to an epitope to inhibit its subsequent recognition by natural antibodies. Methods for altering epitopes on cell surfaces which stimulate hyperacute rejection of the cells by natural antibodies in a recipient subject are described in greater detail in PCT Publication WO/95/33828, published on Dec. 14, 1995, the contents of which are incorporated herein by reference.
The altered (also referred to herein as xe2x80x9cmodifiedxe2x80x9d) retinal cells can comprise an isolated population of cells. The term xe2x80x9cpopulationxe2x80x9d as used herein refers to a group of two or more cells. The population of retinal cells can be neural retina cells, RPE cells and/or iris epithelial cells. In one embodiment, the population of retinal cells is a population of neural retina cells. In another embodiment, the population of retinal cells is a population of RPE cells. The population of RPE cells can be in the form of an intact sheet comprising, for example, an intact monolayer of RPE cells, or in a cell suspension. The term xe2x80x9cintact sheetxe2x80x9d, as used herein, refers to a layer of cells which remain adherent to one another after the cells are harvested. The layer of cells can comprise one or more types of cells including RPE cells. Moreover, for use in transplantation, the population of retinal cells, e.g., neural retina cells or RPE cells, can comprise a relatively pure population of retinal cells. Preferred populations of retinal cells are, therefore, cell populations comprising preferably about 85% retinal cells, more preferably about 90% to 95%, about 98%, 99% retinal cells. The purity of a population of retinal cells can be determined by methods known in the art. For example, markers which specifically detect a particular retinal cell type, e.g., neural retina cells and/or RPE cells, can be used to detect the presence of the retina cell type and then the percentage of those cells in the population can be determined by visual observation. Examples of neural retina cell specific markers include, for example, neuron-specific enolase, interphotoreceptor retinoid-binding protein (IRBP), arrestin, and opsin. RPE specific markers include, for example, cytokeratin 8 and cytokeratin 18.
The modified or unmodified cells described herein can also be grown as a cell culture, i.e., as a population of cells which grow in vitro, in a medium suitable to support the growth of the cells. Media which can be used to support the growth of porcine retinal cells include mammalian culture media, such as those produced by Gibco BRL (Gaithersburg, Md.). The culture media can be, for example, low glucose Dulbecco""s modified Eagle medium (DMEM). Other culture media suitable for the growth of retinal cells include Leibowitz L-15 (with bicarbonate) as described in Jensen et al. (1997) Dev. Biol. 188:267-279, the contents of which is incorporated herein by reference.
B. Retinal Cells Obtained at the Appropriate Age for Transplantation
For use in transplantation studies and treatment of retinal disorders, the retinal cells of the present invention are isolated at the appropriate stage of development in order to allow for growth, reproduction and differentiation following transplantation into an allogeneic or xenogeneic subject. Such retinal disorders include, for example, retinis pigmentosa, phototoxic retinopathy, light damaged retina, macular degeneration, gyrate atrophy, fundus flavimaculatus, Best""s disease, Sorsby""s dystrophy and Stargardt""s disease in humans. Preferred retinal cells are, therefore, neural retinal cells, preferably porcine neural retina cells, more preferably fetal porcine neural retina cells, for use in treating retinis pigmentosa, phototoxic retinopathy, light damaged retina and macular degeneration; and RPE cells, preferably porcine RPE cells, more preferably fetal porcine RPE cells, for use in treating macular degeneration, gyrate atrophy, fundus flavimaculatus, Best""s disease, Sorsby""s dystrophy or Stargardt""s disease. To provide for growth, reproduction and differentiation of porcine retinal cells, and in particular porcine neural retina cells and RPE cells, upon transplantation into a recipient subject, an optimal donor is selected. Typically, retinal cells of the invention are porcine fetal cells which are isolated from porcine fetuses. In one embodiment, the fetal porcine retinal cells are cultured in vitro until they display the desired characteristics for transplantation. For example, in general, RPE cells which are not sufficiently adherent to remain as an intact RPE sheet after harvest are too immature to harvest and transplant. Moreover, in general, neural retina cells which are too immature to harvest and transplant have characteristic morphology. The preferred morphology of RPE cells includes a rounded cell body which is essentially free, preferably free, of surrounding fibroblasts and which the cells are sufficiently adherent to each other such that an intact sheet of RPE cells can be obtained.
Thus, in one aspect of the invention, the porcine retinal cells can be obtained from a fetal pig at selected gestational ages. The retina consists of several layers including the RPE cell layer (which is the most external layer of the retina found in close conjunction with the choriod and choriocapillaris), the layer of rods and cones (i.e., the photoreceptor cells) and the bipolar and ganglionic cells. The RPE cell layer is thought to be a causative agent in the development of macular degeneration which accounts for the build up of metabolic by-products. This layer of cells does not readily replicate in adults, and therefore damage to the RPE layer can be irreversible and lead to the loss of photoreceptors and decreased visual acuity. Therefore, for treatment of retinal disorders, for example, disorders involving abnormal RPE cells, porcine RPE cells are isolated from the retina of a fetal donor swine (also referred to herein as xe2x80x9cpigxe2x80x9d). Preferably, RPE cells are isolated from a fetal pig at a selected gestational age. The selected gestational ages (the total gestation time for pig is 115 days) for isolation of cells was determined based on the following criteria: the ability to specifically dissect RPE cells essentially free, preferably free from fibroblasts, the ability to obtain intact sheets of RPE cells, and the viability of the RPE cells upon isolation. It was discovered that the preferred gestational age of fetal swine from which to obtain RPE cells suitable for transplantation into allogeneic and xenogeneic subjects, e.g., humans, is between about days sixty (60) to sixty-five (65). This preferred gestational age for porcine RPE cells was determined as described in Example I. The results of these experiments demonstrate that RPE cells obtained from swine younger than sixty days are not sufficiently adherent to obtain an intact RPE sheet. Moreover, in fetal swine younger than sixty days, the fibroblast are not as easily separated from the desired RPE cells. However, cells younger than sixty days can be used for transplantation if desired. In addition, the results of cell viability after isolation of cells from the fetuses of varying ages demonstrates that the number of viable RPE cells isolated decreases in fetuses older than about 70 days. Thus, the preferred range for isolation of porcine RPE cells is between about thirty (30) to one hundred (100) days of gestation, preferably about forty (40) to ninety (90) days of gestation. Another preferred range for isolation of porcine RPE cells is between about fifty (50) to eighty (80) days of gestation, preferably about sixty (60) to seventy (70) days of gestation. A particularly preferred age of fetal development for isolation of the porcine RPE cells of this invention is between sixty (60) to sixty-five (65) days of gestation.
The viability of RPE cells can be determined with esterase stain and the presence of proliferating RPE cells in vivo can be determined using Barr labeling as described, for example, in Jones et al. (1997) Invest. Ophth. and Vis. Sci. 38(4):1572. In addition, kits are commercially available which can be used to determine the viability of isolated RPE cells. For example, the LIVE/DEAD Viability/Cytotoxicity Kit, available from Molecular Probes (Eugene, OR) can be used to determine the viability of the isolated RPE cell population.
In addition, the porcine retinal cells, e.g., RPE cells, can be grown as a cell culture until the cells demonstrate the preferred RPE morphology. For example, the RPE cells can be grown in vitro until the cells are sufficiently adherent to obtain an intact RPE sheet. Moreover, the purity of the RPE cells grown as a culture can be determined, for example, by detecting RPE specific markers in culture and then determining by visual observation the percentage of RPE cells in the population. RPE specific markers include, for example, cytokeratin 8 and cytokeratin 18. Such markers can be detected using marker specific antibodies. See, e.g., Nork et al. (1995) Arch. Ophthalmol. 113:791-802. Using such techniques, the purity of such a RPE cell population can, therefore, be determined. In preferred embodiments, the RPE cell population comprises at least about 85% to 90% RPE cells, preferably about 95%, 98%, 99% RPE cells.
C. An Isolated Population of Porcine Retinal Cells
This invention also features an isolated population of cells obtained from porcine retina. For example, retinal cells can be obtained from the ocular globe by hemisecting the globe at the ora serrata and the anterior segment. The neural retina can be separated from surrounding retinal tissue and a population of neural retina cells can be isolated. In addition, the eye cup can be isolated from the porcine retina and RPE cells can be separated from the sclera to obtain a population of RPE cells. As used herein, the term xe2x80x9cisolatedxe2x80x9d refers to a cell or population of cells which has been separated from its natural environment, e.g., removal from the donor animal, e.g., pig, and alteration of the cell""s relationship with neighboring cells in which it is contact. The isolated cell or population of cells can be in the form of a tissue sample, e.g., an intact sheet of cells, e.g., a monolayer of RPE cells, or it can be in a cell suspension. When used to refer to a population of porcine retinal cells, e.g., neural retina cells and/or RPE cells, the term also includes populations of cells which result from the proliferation of the isolated cells of the invention. The term xe2x80x9cpopulationxe2x80x9d is intended to include two or more cells. Cells in a population can be obtained from the same or different source(s), e.g., the same swine or several different swine.
In one aspect of the invention, the population of cells is a substantially pure population of retinal cells. The term xe2x80x9csubstantially purexe2x80x9d as used herein refers to a population of retinal cells comprising at least about 85% to 90% retinal cells, preferably about 95%, 98%, 99% retinal cells. The purity of a retinal cell population, e.g., RPE cell or neural retinal cell population, grown as a culture can be determined, for example, by detecting markers specific for various cell types in culture and then determining by visual observation the percentage of cell types in the population. For example, neural retinal cells can be detected based on the presence of neural cell specific markers such as interphotoreceptor retinoid-binding protein (IRBP), arrestin, and opsin. In addition, RPE cells can be detected based on the presence of RPE specific markers such as cytokeratin 8 and cytokeratin 18. Such markers can be detected using marker specific antibodies. See, e.g., Nork et al. (1995) Arch. Ophthalmol. 113:791-802. Using such techniques, the purity of a retinal cell population can be determined.
Cells obtained from porcine retina can include neural retina cells, RPE cells, iris epithelial cells and/or progenitor cells thereof. Progenitor or precursor cells can be distinguished from committed cells by, for example, differential staining. For example, immature neuroepithelial cells (e.g., neural retinal progenitor cells) express nestin and can be identified with a nestin-specific stain while mature retinal cells such as neural retina cells generally do not express nestin. In addition, mature retinal cells, e.g., neural retina cells, express neuron-specific enolase and can be identified by enolase-specific stain while immature retinal cells, e.g., neuroepithelial cells, generally do not express neuron-specific enolase.
D. Retinal Cells Isolated from Essentially Pathogen-Free Swine
In another embodiment, the retinal cells of the invention are cells determined to be free from at least one organism which originates in the animal from which the cells are obtained and which transmits infection or disease to a recipient subject. Preferrably the cell is determined to be free from at least two organisms. Retinal cells with these characteristics can be obtained by screening the animal to determine if it is essentially free from organisms or substances which are capable of transmitting infection or disease to a xenogeneic recipient, e.g., a human recipient, of the cells. Typically, the cells are porcine cells which are obtained from a swine which predetermined to be essentially free from pathogens which detrimentally affect humans. For example, the pathogens from which the swine are free include, but are not limited to, one or more of pathogens from the following categories of pathogens: zoonotic, cross-placental, neurotropic and ocular-infecting. As used herein, xe2x80x9czoonoticxe2x80x9d refers to organisms which can be transferred from pigs to man under natural conditions; xe2x80x9ccross-placentalxe2x80x9d refers to organisms capable of crossing the placenta from mother to fetus; xe2x80x9cneurotropicxe2x80x9d refers to organisms which selectively infect neural cells; and xe2x80x9cocular-infectingxe2x80x9d refers to organisms which selectively infect cells of the eye. Within each of these categories, the organism can be a parasite, bacterium, mycoplasma, and/or virus. For example, the swine can be free from parasites such as zoonotic parasites (e.g., toxoplasma), cross-placental parasites (e.g., eperythozoon suis or toxoplasma), neurotropic parasites (e.g., toxoplasma), ocular-infecting parasites, and/or mycoplasma, such as M. hypopneumonia. Additionally, the swine can be free from bacteria such as zoonotic bacteria (e.g., brucella, listeria, mycobacterium TB, leptospirillum), cross-placental bacteria (e.g., brucella, listeria, leptospirillum), neurotropic bacteria (e.g., listeria), and/or ocular-infecting bacteria. Specific examples of bacteria from which the swine can be free include brucella, clostridium, hemophilus suis, listeria, mycobacterium TB, leptospirillum, salmonella and hemophilus suis. Additionally, the swine can be free from viruses such as zoonotic viruses, viruses that can cross the placenta in pregnant sows, neurotropic viruses, and ocular-infecting viruses. Zoonotic viruses include, for example, a virus in the rabies virus group, a herpes-like virus which causes pseudorabies, encephalomyocarditis virus, swine influenza Type A, transmissible gastroenteritus virus, parainfluenza virus 3 and vesicular stomatitis virus. Cross-placental viruses include, for example, viruses that cause porcine respiratory reproductive syndrome, a virus in the rabies virus group, a herpes-like virus which causes pseudorabies, parvovirus, a virus that causes swine vesicular disease, teschen (porcine polio virus), hemmaglutinating encephalomyocarditis, cytomegalovirus, suipoxvirus, and swine influenza type A. Neurotropic viruses include, for example, a virus in the rabies virus group, a herpes-like virus which causes pseudorabies, parvovirus, encephalomyocarditis virus, a virus which causes swine vesicular disease, porcine poliovirus (teschen), a virus which causes hemmaglutinating encephalomyocarditis, adenovirus, parainfluenza 3 virus. Specific examples of viruses from which the swine are free include: a virus which causes (or results in) porcine respiratory reproductive syndrome, a virus in the rabies virus group, a herpes-like virus which causes pseudorabies, parvovirus, encephalomyocarditis virus, a virus which causes swine vesicular disease, porcine poliovirus (teschen), a virus which causes hemmaglutinating encephalomyocarditis, cytomegalovirus, suipoxvirus, swine influenza type A, adenovirus, transmissible gastroenteritus virus, a virus which causes bovine viral diarrhea, parainfluenza virus 3, and vesicular stomatitis virus.
In one embodiment, the pigs from which the retinal cells are isolated are essentially free from the following organisms: Toxoplasma, eperythrozoon, brucella, listeria, mycobacterium TB, leptospirillum, hemophilus suis, M. Hypopneumonia, a virus which causes porcine respiratory reproductive syndrome, a virus which causes rabies, a virus which causes pseudorabies, parvovirus, encephalomyocarditis virus, a virus which causes swine vesicular disease, porcine polio virus (teschen), a virus which causes hemagglutinating encephalomyocarditis, suipoxvirus, swine influenza type A, adenovirus, transmissible gastroenteritis virus, a virus which causes bovine viral diarrhea, and vesicular stomatitis virus. The phrase xe2x80x9cessentially free or free from organisms or substances which are capable of transmitting infection or disease to a xenogeneic recipientxe2x80x9d (also referred to herein as xe2x80x9cessentially pathogen-freexe2x80x9d or xe2x80x9cpathogen freexe2x80x9d) when referring to a swine from which cells are isolated or to the cells themselves means that swine does not contain organisms or substances in an amount which transmits infection or disease to a xenogeneic recipient, e.g. a human. Example III provides representative, but not limiting, examples of methods for selecting swine which are essentially free from various organisms. The cells of the invention can be isolated from fetal or post-natal swine which are determined to be essentially free of such organisms. These swine are maintained under suitable conditions until used as a source of cells for transplantation.
Preferred retinal cells isolated from the essentially pathogen free swine include neural retina cells, RPE cells and iris epithelial cells. Optimal gestational ages of the swine from which these cells are isolated are described in detail herein. Porcine retinal cells isolated from essentially pathogen-free swine can additionally be modified to reduce the immunogenecity of the cells upon transplantation into a xenogeneic subject as described herein.
A. Method for Isolating Porcine Retinal Cells from an Essentially Pathogen-Free Swine
Another aspect of the invention pertains to a method for isolating a porcine retinal cell, e.g., a neural retina cell, a RPE cell or a iris epithelial cell, from a pig predetermined to be free from at least two organisms which originate in pig and which are capable of transmitting infection or disease to a xenogeneic recipient of the cells. According to the method, swine are tested for the presence or absence of organisms which are capable of transmitting infection or disease to a xenogeneic recipient, e.g., a human recipient, of the cells. Such pathogens from which the swine are free include, but are not limited to, one or more of pathogens from the following categories of pathogens: zoonotic, cross-placental, neurotropic, and ocular-infecting. Within each of these categories, the organism can be a parasite, bacterium, mycoplasma, and/or virus. The swine can be free from, for example, zoonotic, cross-placental, neurotropic, and/or ocular-infecting parasites or mycoplasma (e.g., M. hypopneumonia). Specific examples of parasites from which the swine are free include: toxoplasma and eperylherozoon. The swine can further be free from, for example, zoonotic, cross-placental, neurotropic, and/or ocular-infecting bacteria. Examples of bacteria from which the swine can be free include brucella, listeria, mycobacterium TB, leptospirillum, and hemophilus suis. Additionally, the swine can be free from viruses such as zoonotic, cross placenta, neurotropic, and/or ocular-infecting viruses. Specific examples of viruses from which the swine are free include: a virus which causes (or results in) porcine respiratory reproductive syndrome, a virus in the rabies virus group, a herpes-like virus which causes pseudorabies, parvovirus, encephalomyocarditis virus, a virus which causes swine vesicular disease, porcine poliovirus (teschen), a virus which causes hemmaglutinating encephalomyocarditis, cytomegalovirus, suipoxvirus, swine influenza type A, adenovirus, transmissible gastroenteritus virus, a virus which causes bovine viral diarrhea, parainfluenza virus 3, and vesicular stomatitis virus. Preferably, retinal cells are isolated from embryos of swine which are predetermined to be essentially free of these organisms.
Methods for isolating retinal cell tissue are known in the art and described herein. For example, RPE sheets can be dissected from eye cups or sheets containing a RPE cell layer and choroid tissue can be obtained, e.g., by dissecting the tissue under a microscope. The RPE cells in the retinal tissue can then be dissociated by chemical means, e.g., enzymes, or by mechanical means, e.g., chopping and/or successive pipette trituration. In addition, neural retina cells can be dissected away from the eye cup and then can be dissociated by chemical means or mechanical means. The swine which are employed in the method of the invention as a source of retinal cells include fetal swine (swine fetuses) and postnatal swine. If a fetal swine is to be used as a source of retinal cells, semen from a boar which has been tested to be essentially free of disease transmitting organisms is employed to artificially inseminate a female swine which is essentially free from such organisms. At a selected gestational age. e.g., the gestational age of a retinal cell type, e.g., a RPE cell, described herein, a hysterectomy is performed under appropriate conditions of sterility and the fetuses are thereafter removed in their individual amniotic sacs. Appropriate retinal cells or tissue are thereafter recovered under appropriate conditions of sterility.
The swine determined to be essentially free from organisms which originate in pigs and which transmit infection or disease to a recipient subject can be employed as a source of a wide variety of cells, e.g., retinal cells. Porcine retinal cells which can be isolated according to this method include, for example, RPE cells and neural retina cells as described in further detail herein. Porcine retinal cells isolated from essentially pathogen-free swine can additionally be modified as described herein.
B. Method for Treating Retinal Disorders of an Allogeneic or Xenogeneic Subject Using Modified Retinal Cells
A still further aspect of the invention pertains to methods for treating retinal disorders in an allogeneic or xenogeneic subject, particularly a human subject, in which retinal cells; e.g., porcine retinal cells, are introduced into the retina, e.g., subretinal space, of the subject. As used herein, the phrase xe2x80x9cretinal disordersxe2x80x9d includes an impairment or absence of a normal retinal cell function and/or presence of an abnormal retinal cell function. For example, an impairment or presence of an abnormal retinal function can result in loss or reduction of visual acuity. The retinal cells, in unmodified form, have at least one antigen on the cell surface which is capable of stimulating an immune response against the cell in a xenogeneic subject. Prior to transplantation, the antigen on the cell surface is altered to inhibit rejection of the cell when introduced into the xenogeneic subject. As used herein, the term xe2x80x9cintroducingxe2x80x9d is used interchangeably with the term xe2x80x9ctransplantingxe2x80x9d. The retinal cells of the invention are introduced into a subject by any appropriate route which results in delivery of the cells to a desired location in the subject. For example, one method of administration of cells into the subretinal space of a subject is by direct injection of the cells using the transvitreal approach. See e.g., Sheng et al. (1990) Invest. Ophthal. and Vis. Sci. 36:381-390; Gouras et al. (1991) Invest. Ophthal. and Vis. Sci. 35:3145-3153. Cells can be administered in a pharmaceutically acceptable carrier, such as a buffered saline solution. Another method which can be used to administer sheets of RPE cells to the subretinal space of a subject is to fold the RPE layer into a specially designed pipette with a tapered gauge for delivery into the subretinal space. The pipette is inserted through a retinotomy and the RPE layer is injected as described in further detail in PCT publication WO 96/26759, published on Sept. 6, 1996, the contents of which are incorporated herein by reference. An xe2x80x9cRPE layerxe2x80x9d as used herein refers to a RPE cell monolayer. Cells which are the be administered as a monolayer, can be stabilized in support matrix such as gelatin as described herein and in PCT publication WO 91/02499, published Mar. 7, 1991, the contents of which are incorporated herein by reference. In addition, other substrates which can be used to stabilize the monolayer include lectins such as concanavalin A and wheat germ agglutin. The number of retinal cells used to treat retinal disorders in a subject depends on the size of the lesion. For example, to treat retinal disorders in a human subject, about 105 to 106 retinal cells of the invention are introduced into the retina, e.g., subretinal space, of the human subject.
The retinal cells of the invention can be inserted into a delivery device which facilitates introduction by e.g., injection, of the cells into the subjects. Such delivery devices include tubes, e.g., catheters, for injecting cells and fluids into the body of a recipient subject. In a preferred embodiment, the tubes additionally have a needle, e.g., a syringe, through which the cells of the invention can be introduced into the subject at a desired location. The retinal cells of the invention can be inserted into such a delivery device, e.g., a syringe, in the form of a solution. Alternatively, the cells can be embedded in a support matrix when contained in such a delivery device. In another embodiment, the cells can be introduced as a monolayer into the subject by harvesting and inserting the cells, as a monolayer, using a pipette with a tapered gauge tip as described in PCT publication WO 96/26759. As used herein, the term xe2x80x9csolutionxe2x80x9d includes a pharmaceutically acceptable carrier or diluent in which the cells of the invention remain viable. Pharmaceutically acceptable carriers and diluents include saline, aqueous buffer solutions, solvents and/or dispersion media. The use of such carriers and diluents is well known in the art. The solution is preferably sterile and fluid to the extent that easy syringability exists. Preferably, the solution is stable under the conditions of manufacture and storage and preserved against the contaminating action of microorganisms such as bacteria and fungi through the use of, for example, parabens, chlorobutanol, phenol, ascorbic acid, thimerosal, and the like. Solutions of the invention can be prepared by using a pharmaceutically acceptable carrier or diluent and, as required, other ingredients enumerated above, followed by filtered sterilization, and then incorporating porcine retinal cells as described herein.
Support matrices in which the retinal cells can be incorporated or embedded include matrices which are recipient-compatible and which degrade into products which are not harmful to the recipient. Natural and/or synthetic biodegradable matrices are examples of such matrices. Natural biodegradable matrices include gelatin and collagen matrices. Synthetic biodegradable matrices include synthetic polymers such as polyanhydrides, polyorthoesters, and polylactic acid. In a preferred embodiment, the support matrix is gelatin.
The methods of the invention are particularly useful for treating human subjects with retinal disorders. Such retinal disorders can be the result of disease, injury, genetics and/or aging. As used herein, retinal disorders include morphological and/or functional abnormality of a retinal cell or a population of retinal cells. Non-limiting examples of morphological and functional abnormalities of retinal cells include physical deterioration and/or death of retinal cells, abnormal growth patterns of retinal cells or the surrounding vasculature, abnormalities in the physical connection between retinal cells with each other or underlying tissue layers (e.g., Bruch""s membrane or choroid tissue), failure of retinal cells such as RPE cells to function as they normally function (e.g., to phagocytize and digest metabolic debris), failure of retinal cells such as neural retinal cells to produce a substance which it normally produces (e.g., rhodopsin or iodopsin) and/or failure of retinal cells such as neural retina cells to initiate visual stimulus. Morphological and/or functional abnormalities of retinal cells are seen with many disorders including, for example, retinis pigmentosa, phototoxic retinopathy, light damaged retina, Sorsby""s dystrophy, Stargardt""s disease and macular degeneration.
In one embodiment of the invention, porcine retinal cells are obtained from fetal pigs. For example, porcine RPE cells preferably obtained from fetal porcine retina at about days sixty (60) to seventy (70) of gestation, are transplanted into the retina, e.g., subretinal space, of a human subject to treat a retinal disorder such as macular degeneration.
Transplantation of retinal cells of the invention into the retina of a human subject having a retinal disorder can result in improved visual acuity and/or reduction of further loss of visual acuity. The term xe2x80x9csubjectxe2x80x9d is intended to include mammals, particularly humans. susceptible to injury-, age-, and/or disease-related retinal disorders. The term xe2x80x9csubjectxe2x80x9d also includes mammals. Examples of subjects include primates (e.g., humans, and monkeys). A xe2x80x9cxenogeneic subjectxe2x80x9d as used herein is a subject into which cells of another species are transplanted or are to be transplanted. Porcine retinal cells are introduced into a subject in an amount suitable to at least reduce or decrease further loss of visual accuity and/or partially correct loss of visual acuity caused by a retinal disorder. Preferred porcine retinal cells are RPE cells and neural retina cells obtained from fetal swine and at selected fetal ages described in detail herein.
Prior to introduction into a subject, the retinal cells can be modified to inhibit immunological rejection. The retinal cells can, as described in detail above, be rendered suitable for introduction into an allogeneic or xenogeneic subject by alteration of at least one immunogenic cell surface antigen (e.g., an MHC class I antigen). To inhibit rejection of transplanted retinal cells and to achieve immunological non-responsiveness in an allogeneic or xenogeneic transplant recipient, the method of the invention can include alteration of immunogenic antigens on the surface of the retinal cells prior to introduction into the subject. This step of altering one or more immunogenic antigens on retinal cells can be performed alone or in combination with administering to the subject of an agent which inhibits T cell activity in the subject. Alternatively, inhibition of rejection of a retinal cell graft can be accomplished by administering to the subject an agent which inhibits T cell activity in the subject in the absence of prior alteration of an immunogenic antigen on the surface of the retinal cell. As used herein, an agent which inhibits T cell activity is defined as an agent which results in removal (e.g., sequestration) or destruction of T cells within a subject or inhibits T cell functions within the subject (i.e., T cells may still be present in the subject but are in a non-functional state, such that they are unable to proliferate or elicit or perform effector functions, e.g. cytokine production, cytotoxicity etc.). The term xe2x80x9cT cellxe2x80x9d encompasses mature peripheral blood T lymphocytes. The agent which inhibits T cell activity may also inhibit the activity or maturation of immature T cells (e.g., thymocytes).
A preferred agent for use in inhibiting T cell activity in a recipient subject is an immunosuppressive drug. The term xe2x80x9cimmunosuppressive drug or agentxe2x80x9d is intended to include pharmaceutical agents which inhibit or interfere with normal immune function. A preferred immunsuppressive drug is cyclosporin A. Other immunosuppressive drugs which can be used include FK506, and RS-61443. In one embodiment, the immunosuppressive drug is administered in conjunction with at least one other therapeutic agent. Additional therapeutic agents which can be administered include steroids (e.g., glucocorticoids such as prednisone, methyl prednisolone and dexamethasone) and chemotherapeutic agents (e.g., azathioprine and cyclosphosphamide). In another embodiment, an immunosuppressive drug is administered in conjunction with both a steroid and a chemotherapeutic agent. Suitable immunosuppressive drugs are commercially available (e.g., cyclosporin A is available from Novartis, Corp., East Hanover, N.J.).
An immunsuppressive drug is administered in a formulation which is compatible with the route of administration. Suitable routes of administration include intravenous injection (either as a single infusion, multiple infusions or as an intravenous drip over time), intraperitoneal injection, intramuscular injection and oral administration. For intravenous injection, the drug can be dissolved in a physiologically acceptable carrier or diluent (e.g., a buffered saline solution) which is sterile and allows for syringability. Dispersions of drugs can also be prepared in glycerol, liquid polyethylene glycols, and mixtures thereof and in oils. Convenient routes of administration and carriers for immunsuppressive drugs are known in the art. For example, cyclosporin A can be administered intravenously in a saline solution, or orally, intraperitoneally or intramuscularly in olive oil or other suitable carrier or diluent.
An immunosuppressive drug is administered to a recipient subject at a dosage sufficient to achieve the desired therapeutic effect (e.g., inhibition of rejection of transplanted cells). Dosage ranges for immunosuppressive drugs, and other agents which can be coadministered therewith (e.g., steroids and chemotherapeutic agents), are known in the art (See e.g., Freed et al. New Engl. J. Med. (1992) 327:1549: Spencer et al. (1992) New Engl. J. Med. 327:1541; Widner et al. (1992) New Engl. J. Med. 327:1556; Lindvall et al. (1992) Ann. Neurol. 31:155; and Lindvall et al. (1992) Arch. Neurol 46:615). A preferred dosage range for immunosuppressive drugs, suitable for treatment of humans, is about 1-30 mg/kg of body weight per day. A preferred dosage range for cyclosporin A is about 1-10 mg/kg of body weight per day, more preferably about 1-5 mg/kg of body weight per day. Dosages can be adjusted to maintain an optimal level of the immunosuppressive drug in the serum of the recipient subject. For example, dosages can be adjusted to maintain a preferred serum level for cyclosporin A in a human subject of about 100-200 ng/ml. It is to be noted that dosage values may vary according to factors such as the disease state, age, sex, and weight of the individual. Dosage regimens may be adjusted over time to provide the optimum therapeutic response according to the individual need and the professional judgment of the person administering or supervising the administration of the compositions, and that the dosage ranges set forth herein are exemplary only and are not intended to limit the scope or practice of the claimed composition.
In one embodiment of the invention, an immunsuppressive drug is administered to a subject transiently for a sufficient time to induce tolerance to the transplanted cells in the subject. Transient administration of an immunosuppressive drug has been found to induce long-term graft-specific tolerance in a graft recipient (See Brunson et al. (1991) Transplantation 52:545; Hutchinson et al. (1981) Transplantation 32:210; Green et al. (1979) Lancet 2:123; Hall et al. (1985) J. Exp. Med. 162:1683). Administration of the drug to the subject can begin prior to transplantation of the cells into the subject. For example, initiation of drug administration can be a few days (e.g., one to three days) before transplantation. Alternatively, drug administration can begin the day of transplantation or a few days (generally not more than three days) after transplantation. Administration of the drug is continued for sufficient time to induce donor cell-specific tolerance in the recipient such that donor cells will continue to be accepted by the recipient when drug administration ceases. For example, the drug can be administered for as short as three days or as long as three months following transplantation. Typically, the drug is administered for at least one week but not more than one month following transplantation. Induction of tolerance to the transplanted cells in a subject is indicated by the continued acceptance of the transplanted cells after administration of the immunosuppressive drug has ceased. Acceptance of transplanted tissue can be determined morphologically (e.g., with skin grafts by examining the transplanted tissue or by biopsy) or by assessment of the functional activity of the graft.
Another type of agent which can be used to inhibit T cell activity in a subject is an antibody, or fragment or derivative thereof, which depletes or sequesters T cells in a recipient. Antibodies which are capable of depleting or sequestering T cells in vivo when administered to a subject are known in the art. Typically, these antibodies bind to an antigen on the surface of a T cell. Polyclonal antisera can be used, for example anti-lymphocyte serum. Alternatively, one or more monoclonal antibodies can be used. Preferred T cell-depleting antibodies include monoclonal antibodies which bind to CD2, CD3, CD4 or CD8 on the surface of T cells. Antibodies which bind to these antigens are known in the art and are commercially available (e.g., from American Type Culture Collection). A preferred monoclonal antibody for binding to CD3 on human T cells is OKT3 (ATCC CRL 8001). The binding of an antibody to surface antigens on a T cell can facilitate sequestration of T cells in a subject and/or destruction of T cells in a subject by endogenous mechanisms. Alternatively, a T cell-depleting antibody which binds to an antigen on a T cell surface can be conjugated to a toxin (e.g., ricin) or other cytotoxic molecule (e.g., a radioactive isotope) to facilitate destruction of T cells upon binding of the antibody to the T cells. See U.S. patent application Ser. No.: 08/220,724, filed Mar. 31, 1994, for further details concerning the generation of antibodies which can be used in the present invention.
Another type of antibody which can be used to inhibit T cell activity in a recipient subject is an antibody which inhibits T cell proliferation. For example, an antibody directed against a T cell growth factor, such as IL-2, or a T cell growth factor receptor, such as the IL-2 receptor, can inhibit proliferation of T cells (See e.g., DeSilva, D. R. et al. (1991) J. Immunol. 147:3261-3267). Accordingly, an IL-2 or an IL-2 receptor antibody can be administered to a recipient to inhibit rejection of a transplanted cell (see e.g. Wood et al. (1992) Neuroscience 49:410). Additionally, both an IL-2 and an IL-2 receptor antibody can be coadministered to inhibit T cell activity or can be administered with another antibody (e.g., which binds to a surface antigen on T cells).
An antibody which depletes, sequesters or inhibits T cells within a recipient can be administered at a dose and for an appropriate time to inhibit rejection of cells upon transplantation. Antibodies are preferably administered intravenously in a pharmaceutically acceptable carrier or diluent (e.g., a sterile saline solution). Antibody administration can begin prior to transplantation (e.g., one to five days prior to transplantation) and can continue on a daily basis after transplantation to achieve the desired effect (e.g., up to fourteen days after transplantation). A preferred dosage range for administration of an antibody to a human subject is about 0.1-0.3 mg/kg of body weight per day. Alternatively, a single high dose of antibody (e.g., a bolus at a dosage of about 10 mg/kg of body weight) can be administered to a human subject on the day of transplantation. The effectiveness of antibody treatment in depleting T cells from the peripheral blood can be determined by comparing T cell counts in blood samples taken from the subject before and after antibody treatment. Dosage regimes may be adjusted over time to provide the optimum therapeutic response according to the individual need and the professional judgment of the person administering or supervising the administration of the compositions. Dosage ranges set forth herein are exemplary only and are not intended to limit the scope or practice of the claimed composition.
The present invention is further illustrated by the following examples which in no way should be construed as being further limiting. The contents of all cited references cited throughout this application are hereby expressly incorporated by reference.